VBA调用相同的C ++ DLL返回不同的结果 [英] VBA call same C++ dll return different results

问题描述

我有一个测试dll函数读取一个字符串并显示它：

  int _stdcall test（LPSTR myString）{
 MessageBoxA（NULL，（LPCSTR）myString，test，MB_OK）; 
 return 0;} 
  

excel VBA声明是

 声明函数test Libtest.dll（ByVal text As String）As Long 
  

有一个子调用该函数。它读取一个值为abcde的excel单元格，并能够显示正确的结果。子代码是：

  sub testCode（）
 test（cells（1,1）.value）
 end sub 
  

然而，当使用excel公式调用dll函数时 = test （A1），消息框只显示字符串的第一个字符a。

我花了整个周末阅读BSTR等，仍然无法解决这个问题。这里发生了什么？

解决方案

将导入的函数声明为私有：

 私有声明函数test_internal Libtest.dll别名test（ByVal text As String）As Long 
  

并为Excel创建一个包装函数：

 公共函数测试（ByVal text As String）As Long 
 Test = test_internal（text）
 End Functin 
  

因为显然，当调用 Declare d API时，VB（A）使用当前系统代码页将字符串参数转换为ASCII， Excel引擎没有。

在附注中，您还可能需要删除括号。

I have a test dll function that reads a string and display it:

int _stdcall test(LPSTR myString) {
MessageBoxA(NULL, (LPCSTR)myString, "test", MB_OK);
return 0;}

The excel VBA declaration is

Declare Function test Lib "test.dll" (ByVal text As String) As Long

There is a sub that calls the function. It reads an excel cell with value as "abcde" and is able to display a correct result. The sub code is:

sub testCode()
    test (cells(1,1).value)
end sub

However when call the dll function using excel formula =test(A1), the message box only display the first char "a" of the string.

I had spent entire weekend reading BSTR, etc, still not be able to solve this. What is going on here?

解决方案

Declare your imported function as private:

Private Declare Function test_internal Lib "test.dll" Alias "test" (ByVal text As String) As Long

and create a wrapper function for Excel to use:

Public Function Test (ByVal text As String) As Long
  Test = test_internal(text)
End Functin

Because apparently, while VB(A) converts string arguments to ASCII using the current system codepage when calling to Declared APIs, the Excel engine does not.

On a side note, you also might want to remove parentheses.

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